In nuclear imaging, one administers a radioactive substance, usually a disease specific biomarker, to a patient and detects emitted radiation with a detector system. Examples of nuclear imaging techniques includes planar nuclear imaging and tomographic nuclear imaging. Planar imaging is performed with a stationary imaging detector (e.g., a flat panel detector for planar scintigraphy) that detects primarily radiation emitted towards one direction, while tomographic imaging is performed with detector systems that detect radiation emitted into a plurality of directions. Examples of tomographic nuclear imaging include, for example, single photon emission computed tomography (SPECT) and positron emission tomography (PET). SPECT can be performed with one or several detectors (e.g., gamma cameras) that can be positioned or rotated around the patient, while PET is usually performed with a stationary imaging detector covering opposite sides of the patient (e.g., a ring detector).
For a nuclear event, the detector systems can detect, for example, the location of the respective detector pixel, the time of detection, and/or the energy of radiation emitted by nuclear events. The detected information (also referred to as nuclear data) is used to reconstruct an image of the distribution of the administered radioactive substance within the patient.
An overview of SPECT and PET systems and iterative image reconstruction for emission tomography is given in chapter 7 and chapter 21 of M. Wernick and J. Aarsvold, “Emission tomography: the fundamentals of PET and SPECT,” Elsevier Academic Press, 2004, the contents of which are herein incorporated by reference. An overview of different reconstruction methods is given in R. C. Puetter et al., “Digital Image Reconstruction: Deblurring and Denoising,” Annu. Rev. Astro. Astrophys., 2005, 43: 139-194, the contents of which are herein incorporated by reference.